Microgravity effects on water supply and substrate properties in porous matrix root support systems.

The control of water content and water movement in granular substrate-based plant root systems in microgravity is a complex problem. Improper water and oxygen delivery to plant roots has delayed studies of the effects of microgravity on plant development and the use of plants in physical and mental life support systems. Our international effort (USA, Russia and Bulgaria) has upgraded the plant growth facilities on the Mir Orbital Station (OS) and used them to study the full life cycle of plants. The Bulgarian-Russian-developed Svet Space Greenhouse (SG) system was upgraded on the Mir OS in 1996. The US developed Gas Exchange Measurement System (GEMS) greatly extends the range of environmental parameters monitored. The Svet-GEMS complex was used to grow a fully developed wheat crop during 1996. The growth rate and development of these plants compared well with earth grown plants indicating that the root zone water and oxygen stresses that have limited plant development in previous long-duration experiments have been overcome. However, management of the root environment during this experiment involved several significant changes in control settings as the relationship between the water delivery system, water status sensors, and the substrate changed during the growth cycles.     

Six-month space greenhouse experiments--a step to creation of future biological life support systems

SVET Space Greenhouse (SG)--the first automated facility for growing of higher plants in microgravity was designed in the eighty years to be used for the future BLSS. The first successful experiment with vegetables was carried out in 1990 on the MIR Space Station (SS). The experiments in SVET SG were resumed in 1995, when an American Gas Exchange Measurement System (GEMS) was added. A three-month wheat experiment was carried out as part of MIR-SHUTTLE'95 program. SVET-2 SG Bulgarian equipment of a new generation with optimised characteristics was developed (financed by NASA). The new SVET-GEMS equipment was launched on board the MIR SS and a successful six-month experiments for growing up of two crops of wheat were conducted in 1996 - 97 as part of MIR-NASA-3 program. The first of these "Greenhouse" experiments (123 days) with the goal to grow wheat through a complete life cycle is described. Nearly 300 heads developed but no seeds were produced. A second crop of wheat was planted and after 42 days the plants were frozen for biochemical investigations. The main environmental parameters during the six-month experiments in SVET (substrate moisture and lighting period) are given. The results and the contribution to BLSS are discussed.